It is one of the promises of the most advanced research in oncology: the possibility, one day (and we still do not know how far), to diagnose a tumor only with a blood sample. we speak, therefore, of liquid biopsy. Where are we at? The answer comes from a study, Pathfinder, just presented at the congress of the European society of oncology (Esmo), which closes today in Paris. The results are promising and confirm what had already been observed in similar previous experiences on the same test, designed to detect the signals in the blood of over 50 types of cancer: the test allowed to discover different forms of cancer in people without symptoms, with the best accuracy and specificity ever.
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How the test works
The exam in question is an MCED test (Test Galleri), an acronym for multi-cancer early detection (literally, early detection of multiple tumors). How does it work? Thanks also to artificial intelligence, the test searches for and identifies the DNA fragments released by cancer cells (ctDna, or circulating tumor DNA) in a blood sample. Once identified, the ctDna is sequenced to search for some particular modifications (anomalous methylations).
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In the Pathfinder Study, the test was used on more than 6,000 apparently healthy people over 50. The test was positive in 1.4% of cases, thus signaling the presence of tumor DNA in 92 volunteers. Among these, a tumor was then actually diagnosed in 35 people (38% of suspected cases), while the false positives were 57. The specificity of the test (ie the ability to give a negative result in healthy subjects) was therefore 99.1% (6,235 out of 6,290 people) and diagnostic confirmation arrived within two months and exclusion within three months for most people tested positive. The doctors have in fact repeated imaging tests after some time, to be sure they can rule out the disease.
The results are an important step in testing the application of this exam in clinical practice. “They show a good detection rate for people who have cancer, around 40%, and an excellent specificity rate for those who don’t have cancer,” notes Deb Schrag, of Memorial Sloan Kettering Cancer Center in New York. (Usa) and first author of the study. “Interestingly, few participants with a false positive screening test required more invasive procedures, such as endoscopies and biopsies. This data should help allay concerns that these tests could lead to a demand for unnecessary procedures in healthy people. “
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It still can’t be screened
Liquid biopsy is now beginning to be used in patients who have already had a tumor to observe its evolution and response to therapies, or to anticipate the onset of relapses as much as possible. To use it as a screening test in healthy people it will be necessary to refine the techniques through other studies. Many are obviously already underway and the road is drawn. the hope is, of course, that of early detection of tumors that are almost always discovered today at an advanced stage, such as that of the pancreas and ovary. “The tests need to be refined so that we can better distinguish tumor DNA from all the other DNA that is circulating in the blood,” Schrag says. “It is also critical to note that the purpose of cancer screening is to reduce cancer mortality. It is premature to draw conclusions on how the MCED test affects mortality, which was not measured in the PATHFINDER study and requires a long follow-up ”.
“We need comparative studies on all types of cancer to find out if an early diagnosis test affects morbidity and mortality,” concludes Fabry André, Research Director at the Gustave Roussy Cancer Center in Villejuif, France, and next president of the Esmo (for the years 2025-2026). We also need to know how tests benefit patients and how to discuss the results with them. Also, we need to learn more about the small percentage of false positive tests. We need some of these answers before we can calculate the cost impact of introducing MCED testing into routine clinical practice. “In the meantime, we must not forget screenings for three cancers – breast, cervical and colon. rectum – which have already been shown to both anticipate diagnosis and reduce mortality.